My last computer retired - 1 month ago. It was more than 5 years old, running Windows XP. XP is still very popular and I would expect it to still be supported and it's 12 years old.
Where did you get your 7 year magic number from?
Of the new software that still claims XP compatibility, much of it requires SP3.
So actually, XP = XP SP3.
Unless you're a large organisation paying a lot of money, you aren't likely to get 5 years of support for a particular version of most products.
http://support.microsoft.com/lifecycle/?LN=en-gb&C2=1173 http://www.microsoft.com/en-us/windows/endofsupport.aspx